Diarylamine antioxidants are known and have been widely used to improve the thermal-oxidative stability and/or light induced degradation in numerous products used in engineering; for example, they can improve the performance properties in lubricants, hydraulic fluids, metal working fluids, fuels or polymers, just to name a few.
Commonly, these diarylamines have been alkylated, see for example, U.S. Pat. No. 2,943,112 which discloses an improved process for alkylating diphenylamine and U.S. Pat. No. 3,655,559 which discloses alkylated diphenylamines as stabilizers. Alkaryl substituted diphenylamines and phenylnapthylamines (such as α-methylstyryl-diphenylamine) are disclosed for example in U.S. Pat. Nos. 3,533,992; 3,452,056 and 3,660,290. Substituted paraphenylene diamines have also been disclosed as antioxidants for lubricants in which iron-catalyzed oxidation reaction can occur, see U.S. Pat. No. 5,232,614.
Additionally, alkyl substituted 1,2-dihydroquinoline and polymers thereof, have been employed as antioxidants, see U.S. Pat. Nos. 3,910,918. While, U.S. Pat. No. 5,310,491 discloses the reaction product of an alkyl substituted 1,2-dihydroquinoline with a diarylamine. Tetrahydroquinones and substituted tetrahydroquinones have also have also been disclosed as antioxidants, see for example U.S. Pat. Nos. 2,794,020; 3,362,929; 4,692,258 and 4,965,006. Likewise decahydroquinolines and substituted decahydroquinolines have been employed as antioxidants, see U.S. Pat. Nos. 2,998,468 and 4,069,195.
In order to satisfy the more severe operating conditions and new applications which require improved oxidation inhibition, continued development of new compounds to mitigate oxidation is of paramount interest. The compounds of the present invention demonstrate superior performance in an organic substrate and thus may serve the continued need.